S. Edwards

Direct reaction analysis of the F19 (p,α0)O16 reaction

Abstract Thirty-two angular distributions of the F 19 (p, α 0 )O 16 reaction over a 23 MeV range were analysed using a plane-wave direct reaction theory incorporating pick-up and exchange pick-up (or heavy-particle stripping) coherently mixed (PWBAE theory). The results of this analysis indicate that the reaction proceeds predominantly by a direct reaction mechanism, but that compound nucleus contributions cannot be ignored at certain energies. Only partial success in obtaining a fit to the extreme backward peak at 11 000 MeV proton bombarding energy, plus the fact that the poorest fits are obtained for other angular distributions with large backward peaking, indicate that other mechanisms than first-order exchange effects are possibly contributing to the backward peaking observed.

Exchange terms in direct nuclear reaction theories

Abstract An internally consistent formulation of the problem of exchange effects in direct nuclear reactions is given. By using convenient Distorted Wave Born Approximation forms, it is shown that in the limit of an infinitely massive target the usual “heavy particle stripping” matrix elements have the scattering properties which the exchange matrix elements should have. It is thus concluded that these forms are correct, and their properties are discussed in plane-wave and other approximations.

Direct reaction analysis of the 15N(p, α0)12C reaction

Abstract Thirty-nine angular distributions of the 15 N ( p , α 0 ) 12 C reaction over a 9 MeV range were analysed using a plane wave direct reaction theory incorporating pick-up and exchange pick-up (or heavy-particle stripping) coherently mixed (PWBAE theory). The results of this analysis indicate that the reaction proceeds predominantly by a direct reaction mechanism.

Optical model analysis of 9Be(p, p0)9Be cross sections and polarizations from 6 MeV to 30 MeV

Abstract Cross-section and polarization data for proton elastic scattering from 9Be in the lab energy range 6 to 30 MeV and in the angular range 20° to 160° have been analyzed using an optical model potential. Good quality fits are obtained with potential parameters which vary smoothly with energy. The effects of energy-averaged compound-nucleus resonances and of quadrupole coupling on the elastic scattering are investigated. The reaction is suggested for use as a polarization monitor since it compares favourably with α(p, p)α for this purpose. Contour maps of polarization, P, and cross section times P2 are given as a function of angle and energy.

Coupled channel analysis of proton scattering from 19F

Abstract Elastic and inelastic differential cross sections measured for protons of incident energies 4.26, 5.96 and 6.87 MeV scattered from 19F are analysed using the adiabatic coupled channel (ACC) approximation. The scattering to the first two, positive-parity states ( 1 2 + and 5 2 + ) of the ground state rotational band are considered, the excitation of negative-parity states being negligibly weak. Using a quadrupole deformation β=0.37 determined from Coulomb excitation measurements, good fits to the 1 2 + and 5 2 + state differential cross sections are obtained by varying only the surface absorption potential with energy, all other parameters being fixed. Comparison with a spherical, optical-model analysis of the same data shows that the latter model overestimates the spin-orbit potential by a factor of 3 compared with the value obtained from the ACC analysis. The effect is related to the large deformation.

Cluster-transfer analysis of the 7Li(3He, p)9 Be reaction

Abstract An exact finite-range two-mode multi-interaction DWBA cluster-transfer analysis of the 7 Li( 3 He, p) 9 Be reaction for 3 He bombarding energies of 3.2, 4.5, and 10 MeV is performed using the computer code FANLU2. It is found that it is essential to include the exchange mode in order to describe the angular distributions at backward angles and that the analysis provides a good overall description of the reaction when the full exact finite-range multi-interaction formalism is employed. Extracted spectroscopic factors indicate that d⊕ 7 Li is a more probable cluster configuration for 9 Be than is 3 He⊕ 6 He, but the latter configuration plays an important role in the analysis. The various cancellation approximations that can be employed in the DWBA are shown to be inadequate for this reaction.

DIRECT REACTION ANALYSIS OF THE

Abstract Thirty-nine angular distributions of the 15 N ( p , α 0 ) 12 C reaction over a 9 MeV range were analysed using a plane wave direct reaction theory incorporating pick-up and exchange pick-up (or heavy-particle stripping) coherently mixed (PWBAE theory). The results of this analysis indicate that the reaction proceeds predominantly by a direct reaction mechanism.

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Abstract Angular distributions of α-particles from the 7Li(3He, α)6Li reaction at 3He bombarding energies of 16 and 18 MeV are analyzed with an exact finite-range two-mode DWBA formalism using the computer code FANLU2. It is demonstrated that within the formalism used it is essential to include the exchange mode of the reaction. The overall features of the angular distributions are described remarkably well, but a strong dependence on optical model parameter sets makes it essential to adhere to a characteristic class of such sets. Spectroscopic factors for direct and exchange modes are extracted and discussed.

N(p,

Abstract It is shown that the behaviour of the angular correlation function symmetry angle φ 0 at backward scattering angles can be taken as evidence for exchange effects in inelastic scattering processes. The observed behaviour of φ 0 for θ > 140° in data from 12 C( α , α ′ γ 4.43 ) and 28 Si( α , α ′ γ 1.77 ) at a bombarding energy of 22.5 MeV is similar to that which has been observed for the exchange mode in mass-transfer reactions. That the corresponding α′ angular distribution data can be well represented by a PWBA exchange mode theory in this region supports this conclusion.

alpha

Abstract Gross effects of intermediate state structure in angular distributions from stripping reactions are investigated using the simple “trapping-state” model of Davis in a planar wave Born approximation stripping theory. The resulting angular distribution is compared with the Butler angular distribution and the data for the reaction 12C(d, p)13C3.85 for a deuteron bombarding energy of 2.80 MeV (lab). It is concluded that this simple model can be expected to be useful in the inclusion of these effects in more sophisticated analyses of such reactions.